Hi-Cy/Flu induces in vivo expansion of NK cells. All patients with AML and renal cell carcinoma were analyzed using an RT-PCR–based chimerism assay when an informative donor allele lacking cross reactivity with the recipient could be established. Shown is the average percent donor PBMC engraftment for each cohort. There was in vivo expansion of donor cells by day 7 in the AML cohort receiving Hi-Cy/Flu (•) but not in the renal cell carcinoma cohort receiving Flu alone (○). Donor cells persisted for 28 days and beyond in some patients.